1. Field of the Invention
Embodiments of the present invention generally relate to methods of cleaning etching reactors.
2. Description of the Related Art
Multiple layers of conducting, semiconducting, and dielectric materials are typically deposited and removed from a substrate during the fabrication of integrated circuits. Known etching techniques, such as wet etching and dry etching, e.g., plasma etching, can be used to remove material from a substrate. Examples of materials that may be removed from a substrate during an etching process include silicon oxides, such as silicon dioxide (SiO2), SiCH3, and other dielectric materials, such as low dielectric constant (low k) materials, e.g., carbon-doped oxides, polyimides, polytetrafluroethylenes, parylenes, polysilsesquioxanes, fluorinated poly(aryl ethers), and fluorinated amorphous carbon.
Etching processes are typically performed in etching reactors. A conventional plasma etching reactor includes a reactor chamber and an apparatus for producing a plasma within the reactor chamber. Etching processes typically include the use of a plasma of fluorine-containing gases, such as CHF3, CF4, C4F6, C4F8, and CH2F2 to remove material from a substrate. While fluorine is an effective etchant, fluorine can also etch and damage the surfaces of the plasma etching reactor chamber during etching processes. When fluorine attacks the surfaces of the chamber, it can react with components of the chamber surfaces to form contaminants on the chamber surfaces. For example, fluorine can react with an Al2O3 chamber surface and form contaminating AlFx particles, such as AlF3. Other contaminants that may form on the chamber surface include CxFy and residues that contain fluorine, carbon, oxygen, and/or hydrogen and are referred to as fluorocarbon polymers. Over time, the contaminants may dislodge from the chamber surfaces, land on a substrate in the chamber, and contaminate the substrate. Even if the contaminants do not directly impact a substrate, the presence of the contaminants on the chamber surfaces can affect the etching processing environment. Generally, it is believed that the plasma processing conditions within an etching reactor are a result of current processing conditions and prior processes that may leave a “memory effect” or a “chamber history effect,” such as the contaminants described herein. For example, fluorine from fluorine-containing contaminants that were embedded in the chamber surface during a previous etching process may leach out of the chamber surface during a subsequent fluorine-based etching process. The fluorine leached from the chamber surface increases the effective concentration of fluorine during the etching process, which may increase, or otherwise change, the etching rate. The changes to the etching process from substrate to substrate due to a memory effect degrade the etching process uniformity and reliability. Uncontrolled changes in etching can lead to changes in device geometries and dimensions of semiconductor substrates.
Methods of cleaning etching reactors to remove contaminants generated during etching have been developed. Methods of cleaning an etching reactor include physically, i.e., manually, cleaning the reactor, wet cleaning, and using a plasma from a fluorine-containing gas or from a fluorine-containing gas and oxygen gas to clean the reactor. Physically cleaning a reactor typically requires reactor downtime, which lowers substrate throughput. Wet cleaning processes can be used, but they are typically time consuming and cannot be performed after only one or several substrates are etched. Furthermore, wet cleaning processes are not effective in removing all of the fluorine that remains in the chamber after etching. A plasma from a fluorine-containing gas or from a fluorine-containing gas and oxygen gas is typically effective in removing some contaminants from a reactor. However, a plasma from a fluorine-containing gas or from a fluorine-containing gas and oxygen gas generally does not remove the desired amount of fluorine and other contaminants from the reactor. Therefore, there remains a need for methods of effectively cleaning plasma etching reactors.